Android Question Google Cloud Message (GCM), what about the collapse key?

Is the collapse key-field necessary in my push-app? I have read something about it in the documentation of the old C2DM. The collapse key is deciding, if the client gets all notification or only the last one. In my app, I don't use the collapse key, but it is important for me to make sure, that the client gets every push-notification. Do I have to set this field?

Thanks for help....